The present invention relates to a manually guided implement having an internal combustion engine and a carburetor for supplying a fuel/air mixture to the internal combustion engine.
Manually guided implements, such as chain saws, brush cutters, trimmers, suction or blower devices, or the like, having an internal combustion engine are used outdoors under changing climatic conditions. Thus, a carburetor must provide an optimally adjusted fuel/air mixture for operation of the internal combustion engine in a wide temperature range as well as at different levels of humidity. At high atmospheric temperatures, it is desirable to draw in through the carburetor fresh air that is as cool as possible, since the cool air has a high density, and the internal combustion engine has a corresponding efficiency. However, if the temperature is close to freezing, carburetor icing can occur, whereby an ice layer forms in the region of a Venturi section or at the fuel nozzles in the carburetor. The ice layer adversely affects the formation of an optimum fuel/air ratio, and can lead to shut down of the internal combustion engine.
To avoid carburetor icing, a number of devices are known according to which intake air is guided past hot portions of the internal combustion engine and is drawn in through the carburetor. Due to the increased temperature, however, the intake air has a relatively low air density, which adversely affects the power of the internal combustion engine. A switching device for the selective supply of cool or warm intake air, as well as a corresponding guidance of air past hot parts of the engine and through an air filter and the carburetor, is structurally complicated and expensive.
It is therefore an object of the present invention to provide a manually guided implement having an easy to operate carburetor preheating.